C:/Program Files/LimeWire/Shared
That's where your files are stored. Go there and play them from there.
Codecs. You need them. Some vids won't play without'em. You can either download the nimo pack (Yo, anybody. We need a fresh nimo-pack link here!) or get one of these two (free) players:
VLC Mplayer
Those will play most everything you throw at them (and many more)